Showing papers on "Collimated light published in 1990"

Apparatus for and method of performing stereotaxic surgery

Abstract: A method and an apparatus are set forth for selectively irradiating a target within a patient A 3-dimensional mapping is provided of a mapping region surrounding the target A beaming apparatus emits a collimated beam Diagnostic beams at a known non-zero angle to one another pass through the mapping region They produce images of projections within the mapping region Electronic representations of the images are compared with the reference data thereby locating the target The relative positions of the beaming apparatus and the living organism are adjusted in such a manner that the collimated beam is focused on the target region The comparison is repeated at small time intervals and, when the comparison so indicates, the adjusting step is repeated, as needed, and in such a manner that the collimated beam remains focused on to the target region

Free‐space radiation from electro‐optic crystals

Abstract: We describe a technique to extract electro‐optic Cherenkov radiation from a LiTaO3 crystal into free space. This permits the generation of collimated beams of terahertz radiation into free space and overcomes previous limitations imposed by total internal reflection.

Modeling light reflection for computer color vision

Abstract: In computer vision applications, analysis of shading information requires a proper model of light reflection from object surfaces. To overcome the shortcoming of the most often used model and to extend the reflection model for computer color vision, an examination is made of the light reflection problem using the bidirectional spectral-reflectance distribution function (BSRDF) to specify both incident- and reflected-beam geometries. It is shown that the product form can still be retained for a polychromatic light source under two lighting conditions: the light source is collimated; or the spectral factor and the geometric factor can be separated for both the light source and the BSRDF of the surface. The reflection model is then applied to the formulation of a neutral-interface-reflection model, which is tested experimentally. The results show the adequacy of this type of model for surfaces of some material compositions, e.g. plastics, plant leaves, painted surfaces, orange peels, and some glossy cloth, but not for others, e.g. colored paper and some ceramics. >

Optical system with bright light output

Abstract: An optical system producing bright light output for optical pumping, communications, illumination and the like in which one or more fiberoptic waveguides receive light from one or more diode lasers or diode laser bars and transmit the light to an output end where it is focused or collimated into a bright light image. The input end of the fiberoptic waveguide may be squashed into an elongated cross section so as to guide light emitted from an elongated light source such as a diode laser bar. The waveguides are preferably arranged at the output end into a tightly packed bundle where a lens or other optical means focuses or collimates the light. For diode laser bars much wider than 100 microns, a plurality of waveguides may be arranged in a line to receive the light, and then stacked at the output in a less elongated configuration. In this manner, light from many diode lasers or laser bars may be coupled through the bundle into the end of solid state laser medium.

Multipass cell for molecular beam absorption spectroscopy.

Abstract: We report a two-spherical mirror multipass cell which allows efficient coupling of a laser beam to a collimated molecular beam at the center of the cell. With near-concentric alignment and the laser beam coupled into and out of the cell at the edges of opposite mirrors, an approximately parabolic pattern of reflections is observed on each mirror. Aligned for forty to fifty passes, the cell is used for direct absorption spectroscopy of jet-cooled acetylene, propyne, and 1-butyne in the 3-μm region. Sub-Doppler linewidths as narrow as 12 MHz have been recorded.

Atomic force microscope

Abstract: An atomic force microscope comprises a probe having a sharply-pointed tip end. The probe is supported on the free end portion of a cantilever and is close to the surface of a specimen. When an interatomic force is produced, the cantilever is deformed, and the probe is displaced. The displacement of the probe is detected by an optical system. A light beam emitted from a light source is collimated by a lens, and reflected by a polarized beam-splitter, and also by a half-mirror. Then, the light beam passes through a quarter wavelength plate and an objective lens, such that the light is converged on the cantilever. The reflected light beam from the cantilever returns along the same optical path and passes through the splitter. The light beam is divided into two light beams at the splitter. These two light beams are reflected by respective prisms and are then incident on respective photodetectors. These photodetectors detect the displacement of the probe.

Collimation apparatus for x-ray beam correction

Abstract: A computed tomography system corrects image errors resulting from misalignment of the fan beam as a result of placement of the x-ray tube, thermal drift of the x-ray tube anode of mechanical stresses of the gantry or x-ray tube. Misalignment is determined alternately by means of a z-axis offset detector which detects movement of the exposure area of the CT fan beam or a predictive model that calculates thermal drift of mechanical deflection of the focal spot of the x-ray tube based on previous use. The system includes a collimator with a controllable z-axis position which may be controlled to reduce z-axis offset of the fan beam exposure area or to make the fan beam more parallel with the imaging plane of the CT system.

Method and apparatus for analyzing the appearance features of a surface

Abstract: A method and apparatus for analyzing the appearance features of a surface with a spatially coherent beam of uniformly distributed collimated polychromatic light that is directed through a beam limiting means (or mask) and onto the surface at an acute angle of incidence. A scanned imaging detector, translatable through a sequence of focal plane positions along the optic axis between the mask and surface, measures the reflectance values associated with the scanned pixel intensities. After standardization, the scan intensity values are Fourier transformed into the spatial frequency domain to obtain an optical transfer function (OTF) and power and amplitude spectra. The visual spatial frequency response characteristic V(f) and standard psychophysical methodology is applied to mathematically determine surface appearance attributes such as orange peel, microwrinkle, cracks and crazes, distinctness of image (DOI), gloss, haze, contrast, luster, fog and texture.

Agile beam steering using binary optics microlens arrays

Abstract: Agile steering of a helium-neon laser beam (X = 632.8 nm) has been demonstrated using a complementary pair of 5-cm-aperture binary optic microlens arrays in the Galilean telescope geometry. Segmentation of a collimated input beam by illuminating approximately 60,000 /5 microlenses of 200-jim diameter and parabolic phase profile results in nearly aberration free beam steering over an 1 1° field of view for 100- pm lateral displacements of one array relative to the other. Wavefront quality and steering efficiency of the deflected beam has been measured as a function of steering angle and is compared to a simple theoretical model.

Three-dimensional maximum-likelihood reconstruction for an electronically collimated single-photon-emission imaging system

Abstract: A three-dimensional maximum-likelihood reconstruction method is presented for a prototype electronically collimated single-photon-emission system. The electronically collimated system uses a gamma camera fronted by an array of germanium detectors to detect gamma-ray emissions from a distributed radioisotope source. In this paper we demonstrate that optimal iterative three-dimensional reconstruction approaches can be feasibly applied to emission imaging systems that have highly complex spatial sampling patterns and that generate extremely large numbers of data values. A probabilistic factorization of the system matrix that reduces the computation by several orders of magnitude is derived. We demonstrate a dramatic increase in the convergence speed of the expectation maximization algorithm by sequentially iterating over particular subsets of the data. This result is also applicable to other emission imaging systems.

Helmet mounted display

Abstract: A holographic objective system (3) produces an intermediate real image (4) of information displayed on an electrically addressable spatial light modulator or SLM (1), the real image (4) being collimated by a powered holographic reflector (5) constructed as part of the visor of a helmet worn by the viewer (9). The SLM (1) is illuminated by laser light from a remote laser (8) via a single optical fibre (6) and beam splitter (2). A diffuser (7) is provided either between the laser and the beam splitter or in the plane of the intermediate image (4). The objective system (3) may alternatively include, or consist entirely of, conventional optical elements.

Method and apparatus for determining the physical properties of materials using dynamic light scattering techniques

Abstract: A system for determining the physical properties of materials through the use of dynamic light scattering is disclosed. The system includes a probe, a laser source for directing a laser beam into the probe, and a photodetector for converting scattered light detected by the probe into electrical signals. The probe includes at least one optical fiber connected to the laser source and a second optical fiber connected to the photodetector. Each of the fibers may adjoin a gradient index microlens which is capable of providing a collimated laser beam into a scattering medium. The position of the second optical fiber with respect to the optical axis of the probe determines whether homodyne or self-beating detection is provided. Self-beating detection may be provided without a gradient index microlens. This allows a very small probe to be constructed which is insertable through a hypodermic needle or the like into a droplet extending from such a needle. A method of detecting scattered light through the use of a collimated, Gaussian laser beam is also provided. A method for controlling the waist and divergence of the optical field emanating from the free end of an optical fiber is also provided.

Liquid crystal display apparatus providing improved illumination via trucated prisms

Abstract: Illuminating light from a light source is reflected by a reflector and collimated by a condenser lens and then applied onto the back of a liquid crystal cell. The liquid crystall cell has attached on its light source side an optical sheet which consists of a large number of optical elements such as convex or concave lenses aligned with picture elements or pixels of the liquid crystal cell. The optical elements each converge the rays of light from the light source onto each of the pixels, so that the rays that would otherwise strike a matrix circuit section and a black matrix layer will be focused on and passed through the pixels. This enhances the brightness of an image formed on the front of the liquid crystal cell and also prevents temperature rise in the liquid crystal cell because the black matrix layer and the matrix circuit section, components of the liquid crystal cell, are not struck and heated by the incoming light rays.

Electrically addressable liquid crystal projection system with high efficiency and light output

Abstract: An improved polarized color video projector incorporates a light source to provide three collimated beams of linearly polarized light of blue, green, and red colors A light modulator capable of imparting a video image in a light beam is positioned in each of the three colored beams to modulate the individual colored image components in each of the beams A dischroic beam recombiner receives the modulated blue and green beams, and recombines them into a combined blue and green color image carrying beam A polarization-selective/beam analyzer/recombiner receives the recombined blue and green beam and recombines it with the red beam A retarder placed between the light modulator for the red beam and the polarization-selective/beam analyzer/recombiner, in the path of the modulated red beam, rotates the plane of polarization of the red beam to allow it to be recombined with the recombined blue and green beam in the polarization-selective/beam analyzer/recombiner Projection apparatus receives the recombined blue, green, and red beams and projects them onto a display screen

Experimental cataract induced by ultraviolet radiation.

Abstract: The purpose of the present work was to increase the understanding of the toxic effects of ultraviolet radiation on the lens. A high-pressure mercury arc source with collimating optics, an interference filter (Tmax = 300 nm, T0.5 = 10 nm) and projecting optics was employed for experimental exposure of animals. Irradiance was measured with a calibrated photodiode. A device for objective absolute measurement of light dissemination in rat lenses was developed and characterized on a reference sample of lenses from healthy rats. A tolerance limit for non-pathological was set on a statistical basis. A method for preparing lens samples for atomic absorption spectrophotometry was developed and characterized. In vivo exposure of rat lenses to 6 kJ/m2 induced unscheduled DNA synthesis and reduced scheduled DNA synthesis. Microscopic observation, with a phase contrast microscope, of rat lenses demonstrated that in vitro exposure to 0.72 and 2.9 kJ/m2 evoked anatomical alterations in the lens epithelial cells and accelerated the swelling observed in incubated lenses. Lenses exposed to 36 kJ/m2 in vivo opacified completely in one week. The exclusively white opacification started at the anterior surface. As observed light and electron microscopically the lens cells swelled, starting in the epithelium and thereafter involving first the anterior cortex, later the posterior cortex and finally, within a week after exposure, the outer nuclear region. Light dissemination in the lens after exposure to 30 kJ/m2 increased exponentially with a 5.5 h latency before onset, and a time constant of 19 h. The water mass in the same lenses increased transiently with a maximum 24 h after exposure. The expected increase in lens dry mass due to growth did not take place. Rabbit lenses were incubated after exposure in vitro to 0.6, 3.0 and 6.0 kJ/m2, respectively. The two higher doses induced quicker mass gain in exposed lenses than in their non-exposed contralaterals. There is an increase in sodium in lenses exposed to 30 kJ/m2 and a simultaneous decrease in potassium. The sodium increased exponentially with a 6.6 h latency before onset, and a time constant of 38 h. A slight increase in light dissemination and in sodium per dry mass was noted even in the non-exposed lenses contralateral to those exposed. The data collected suggest that the opacification seen after a high-dose exposure of the lens to 300 nm UVR in vivo occurs as a result of osmotic swelling.

Apparatus and method for normal incidence reflectance spectroscopy

Abstract: An external reflectance spectroscopy apparatus and method are disclosed in which maximum radiation througput is obtained by using a beamsplitter which reflects half of a collimated beam and transmits the other half. In order to obtain reliable results, the condition of perpendicular incidence on the sample is approximated (without limiting throughput) by providing a beamsplitter having an uneven number of reflecting blades and the same number of transmitting openings. Each reflecting blade is opposite to an open area having the same size and shape. The result is a substantial equalizing of contributions from rays polarized parallel to the plane of incidence and from rays polarized perpendicular to the plane of incidence.

Experimental test-object study of electronically collimated SPECT.

Abstract: The imaging performance of a prototype electronically collimated single-photon emission computed tomography (SPECT) camera comprising a unique 4 x 4 germanium detector backed by an uncollimated scintillation camera has been evaluated. Three-dimensional images of cylindrical test-objects containing either 99mTc (140 keV) or 137Cs (662 keV) are reported. Electronically collimated counts were acquired from the objects rotated to 20 or 40 angular positions in front of the germanium detector to simulate a cylindrical scanning system. For comparison, mechanically collimated data were also acquired from the test-objects. The SPECT images show a slightly better resolution for mechanical over electronical collimation (1.3 +/- 0.25 cm mechanical, 1.5 +/- 0.25 cm electronical at 140 keV; 1.5 +/- 0.25 cm mechanical, 1.7 +/- 0.25 cm electronical at 662 keV). The equi-resolution sensitivity, however, was deduced to be approximately an order of magnitude higher with electronic collimation to image a head-sized object using 99mTc. In addition, the sensitivity gain increases with increasing energy, suggesting the unique potential of electronic collimation in high-energy SPECT.

Picosecond time‐resolved surface‐lattice temperature probe

Abstract: Picosecond reflection high‐energy electron diffraction is used as a time‐resolved surface‐lattice temperature probe. A picosecond laser pulse is split into two beams. The first interacts with the sample. The second activates the cathode of an electron gun creating a collimated and focused electron pulse that is well synchronized with the heating laser pulse. The electron pulse is used to generate a reflection high‐energy electron diffraction pattern of the sample. Since heating results in an intensity reduction of the elastically scattered electrons (Debye–Waller effect), the diffraction pattern provides information on the surface temperature as well as structure. Time‐resolved measurements of the picosecond laser‐heated surface show general agreement with a heat diffusion model.

Three dimensional display system

Abstract: A three dimensional display system includes a laser for generating a laser light signal. The signal is expanded and collimated using a traditional lens system and is directed to an acousto-optic modulator wherein it is modulated to generate a three dimensional image such as a holographic image. The modulation signal for the modulator is provided by a data processing system. The data processing system applies signals to the modulator that encode a diffraction pattern. The diffraction pattern is realized by the modulator upon application of the signals and the three dimensional image is produced by the modulated light signals. The image is demagnified by a demagnifier, and subsequently, imaged by a viewing lens. A horizontal scanner continuously multiplexes segments of the holographic image and compensates for the motion of segments across the modulator. A vertical scanner is provided to properly vertically position horizontal lines of the holographic image.

Micro-echographic probe for ultrasound collimation through a deformable surface

Abstract: The present invention relates to a micro-echographic probe for ultrasound collimation through a deformable surface. The probe comprises at one end an ultrasonic wave beam transducer, disposed, for example, in the form of a spherical cap, so that said beam converges in a focus (A), which focus is also that of the other end of the monolithic body and which is the contact tip, so that the beam which penetrates in the body to be analyzed is collimated. The ultrasonic waves are preferably at a frequency equal to at least 50 MHz.

Catadioptric projector, catadioptric projection system and process

Abstract: Catadioptric area-of-interest display projectors (1) produce displays having resolution of substantially less than 10 arc minutes per line over a wide field of view. Such projectors (1) include an external entrance pupil (21) for receiving images of substantially collimated light, and optics (2-17) for conveying such light onto and through an opening (19) in the surface (35) of an aspheric mirror (18), and then through an opening (20) in a spherical mirror (33) so that light emerging from the opening (20) in the spherical mirror (33) is displayed on a curved screen surface with such high resolution. A projector system includes this projector (1) and a mirror for steering collimated light from the entrance pupil (21) of the projector (1) into the projector optics. This system, when placed in a flight simulator at the periphery of a flight simulator dome for projection of such light images onto the inner curved surface of the dome, provides high resolution images to viewers located at the center of the dome.

Resolution improvement in flying spot scanner

Abstract: An improved flying spot scanner (48, 68) is disclosed, which is particularly applicable to use with a raster output scanner (ROS). The primary scan provided by an ROS is a continuous scan of the optical beam (26) along the scan line (40). The present invention provides a discontinuous pixel-by-pixel scan in the opposite direction to the continuous primary scan. Thus each pixel is positioned statically at its correct location on the photoreceptor (54) during the pixel's duration. At the end of each pixel's duration, the beam snaps rapidly to the position of the next pixel. Use of this invention will form a non-blurred image of each pixel on the photoreceptor (54). The invention uses an optical deflector (50, 70) to drive the beam opposite to the direction of the primary beam scan during each pixel's duration. The optical deflector (50, 70) may be an angle deflector (50) when used in a collimated optical beam (60), or it may be a translation deflector (70) when used in a non-collimated optical beam (72). This invention provides a flying spot scanner (48, 68) in which all the gray scale detail and resolution available in a pixel is preserved, with no smearing or blurring of pixels, independent of the content of adjacent pixels.

Collimation optical system especially for helmet display device

Abstract: PURPOSE: To remove the cause of aberration an to improve the quality of a video by making a 1st mirror reflective and a 2nd mirror partially transparent. CONSTITUTION: This collimation optical system is constituted of a device for generating an optical video or a light source 1, an objective collimating lens or a collimator 2, a 1st parabolic mirror 4 and a 2nd parabolic mirror 5 in order along the same optical path. The mirrors 4 and 5 form a confocal system, and the mirror 4 is a total reflection mirror and the mirror 5 is translucent so as to make radiation from outside landscape pass. the mirrors 4 and 5 are put at the end of a photocoductor formed of a plate 10 made of transparent material having two parallel surfaces, and form the confocal optical system for enlarging 1. Thus, wider visual field is obtained while holding the accurate quality of the video.

Apparatus and method for laser beam diagnosis

Abstract: An apparatus and method is disclosed for accurate, real time monitoring of the wavefront curvature of a coherent laser beam. Knowing the curvature, it can be quickly determined whether the laser beam is collimated, or focusing (converging), or de-focusing (diverging). The apparatus includes a lateral interferometer for forming an interference pattern of the laser beam to be diagnosed. The interference pattern is imaged to a spatial light modulator (SLM), whose output is a coherent laser beam having an image of the interference pattern impressed on it. The SLM output is focused to obtain the far-field diffraction pattern. A video camera, such as CCD, monitors the far-field diffraction pattern, and provides an electrical output indicative of the shape of the far-field pattern. Specifically, the far-field pattern comprises a central lobe and side lobes, whose relative positions are indicative of the radius of curvature of the beam. The video camera's electrical output may be provided to a computer which analyzes the data to determine the wavefront curvature of the laser beam.

Laser-based wheel alignment system

Abstract: A device and method to align the wheels of motor vehicles. A beam of collimated light from a low power visible laser is split into two generally parallel beams by a partially transmitting mirror and a series of plane front surface mirrors positioned in front and along side the vehicle being serviced. The two beams are reflected from a set of plane mirrors attached to the rims of the wheels to be aligned. The vertical and horizontal angles of each of the wheel-mounted mirrors are set by calibrated lead-screws to cancel the angular displacement of the wheels expected when the wheels are properly aligned. The reflected beams are imaged through a large aperture beam combiner on a common viewing screen. Correct toe-in and camber settings are indicated when the laser beams reflected from the wheel-mounted mirrors overlap at the center of the viewing screen. The caster settings of the front wheels are measured by observing the angle at which the reflected spots travel across the screen when the steering wheel is turned the system can be used to align the front wheels only, or alternatively all four wheels simultaneously.

Detection system for Raman scattering employing holographic diffraction

Abstract: The Raman scattering detector of this invention includes a source of collimated monochromatic illumination, a cube formed of two right angle prisms, a holographic optical element disposed between the prisms, a concentrating lens, a focusing lens and one or more photo detectors. The illuminating beam passes through the cube and is concentrated by the concentrating leans to a sample. Scattered light returned to the concentrating lens is substantially collimated upon return to the cube. The holographic optical element diffracts light at desired Raman wavelengths approximately 90 degrees without substantially affecting the original wavelength. The holographic optical element further disperses light at desired Raman wavelengths permitting them to be separated. The diffracted and dispersed wavelengths are focused on one or more detectors by the focusing lens.

Ultrahigh vacuum picosecond laser‐driven electron diffraction system

Abstract: A laser‐driven picosecond time‐resolved electron diffraction system operating in ultrahigh vacuum is described. A picosecond laser pulse is split into two beams. The first interacts with the sample under study. The second activates the cathode of an electron gun creating a collimated and focused electron pulse that is well synchronized with the heating laser pulse. By spatially delaying the part of the laser pulse that photoactivates the cathode from that which irradiates the sample, the electron pulse can be set to arrive at the sample at a specific time after sample irradiation. When a flat smooth sample is aligned such that the electrons are in grazing incidence on its surface, a reflection high‐energy electron diffraction pattern of its first few atomic layers is generated. Analysis of the diffraction pattern provides information on the surface structure and temperature at a set time lapse between the arrival of the laser and the electron pulse to the sample. Design, characterization, and operation of this system along with an example of its application to monitor the transient surface temperature using the surface Debye–Waller effect are discussed.

Semiconductor laser apparatus

Abstract: In a semiconductor laser apparatus of the invention, a laser beam emitted from a semiconductor laser is collimated by an optical leans, and is subsequently split by a beam splitter in two directions. One split laser beam component is focused on a first photodetector through an optical lens. The other laser beam component is incident on a Fabry-Perot resonator, and is changed in intensity thereby. The laser beam component is then focused on a photodetector through an optical lens. The Fabry-Perot resonator is integrally designed such that dielectric multilayer films are respectively deposited on both the end faces of a crystalized quartz bulk, which is shaped into a columnar shape extending in the C-axis direction, so as to form a pair of reflect filters. Since the bulk is made of crystalized quartz it is not easily influenced by changes in temperature.

Pulsed delivery of laser energy in experimental thermal retinal photocoagulation

Abstract: Retinal lesions produced with a pulsed laser beam of 1-20 kHz frequency and 10-100% duty cycle were compared with lesions produced with a continuous wave (cw) laser of the same peak power and total energy. Photocoagulation was applied to the retina of three black pigmented rabbits using krypton red laser (647.1 nm) equipped with an acousto-optical modulator to convert cw laser emission to a pulsating beam. An optical fiber fed the laser beam into an optical system delivering a collimated beam of predetermined divergence; the animal's eye focused this beam to a 50-pm spot on the retina. Peak power was kept constant at 0.2 W, and energy was kept constant at 20 mJ. After 7 months the animals were sacrificed and retinal tissue examined by light microscopy. The central section of each lesion was identified and photographed. For lesions with the same energy per pulse and the same pulse duration, the most influential factor, in the frequency range of 1-20 kHz, appeared to be the duty cycle: the smaller the duty cycle, the smaller the lesion, and vice versa. In other words, the shorter the time interval between consecutive pulses, the larger were the pulsed laser lesions.

Spatial light modulator with improved aperture ratio

Abstract: A spatial light modulator is disclosed with a first lens array disposed adjacent to a matrix of light modulators, and in proximity to a liquid crystal light valve containing a photoconductive element. Low intensity light is collimated by a lens element to illuminate an optical aperture which has geometric configuration similar to that of the matrix element. The first lens array focuses light from the illuminated aperture into the pupil of a matrix addressed spatial light modulator element. The second lens array collects light emitting from the light modulator element, and focuses the image of the aperture onto the photoconductive element of the liquid crystal light valve so as to preserve the geometrical and positional configuration of the optical aperture, and magnify the size of the illuminated region on the photoconductor. The design of the optics is such that when adjacent apertures are imaged onto the photoconductor, the proximate boundaries of the illuminated regions are contiguous.